When you sign onto your online account and land on the Tax Home web page, scroll down and click on Add a state. See screenshot
This will take you back to the 2018 online tax return where you can make any corrections needed.
Did your efile reject? Why? It wouldn't be for the EIC but maybe for the wrong 2017 AGI?
When did you file 2017? If it was late in the year try putting in zero for the AGI. And see,
If you can’t get it to efile you will have to print and mail it.
How to correct the AGI